This invention relates to information processing and communication systems and, more particularly, to digital addressing arrangements for such systems wherein the address messages are transformed at selected locations while propagating through the system.
It is a common practice in the present state of the digital data processing and communications art to transmit and receive digital information on a common communication link between a multiplicity of subsystems, computers, remote terminals or stations, peripheral devices, sensors or output devices, and the like. At a main device or controller of such systems, each peripheral or associate device is uniquely accessed by transmitting a selected one of a plurality of access messages over a common address link to the associate devices. Two conventional arrangements are generally used to obtain this practice.
First, the address link is connected in the same identical manner to each of the associate devices. Each associate device at any one of the connections to the address link must be specially designed to recognize and/or originate a particular access message. This arrangement offers the advantage of having identical address links between the devices so that the unique property of an access message is the characteristic of the associate device rather than the connection thereto of the address link. The disadvantage is that the associate devices are unique and not interchangeable.
Another arrangement is to have a unique subset of a group of conductors comprising the address link connected to each associate device. The advantage of this arrangement is that the unique characteristic of each associate device is a property of the connection thereto enabling all the associate devices to be identical and thus interchangeable. The disadvantages are that such an arrangement is rather inflexible and is susceptible to craft errors in making the connections.
A primary object of the present invention is to provide an addressing arrangement for a main device and a plurality of identical associate devices that are identically connected to an address link and yet have each associate device uniquely identified by the main device.
A related object is to provide an addressing arrangement that is readily and simply implemented.
A further object is to provide an addressing arrangement wherein a universal access message feature is efficiently provided and the unique access message of a particular associate device is the same whether that device is the originator or recipient of information on the common communication link.